In general, a water tank in which live fishes are accommodated, should be maintained at a constant water temperature so that an inhabited environment of the live fishes can be maintained with good quality. It is not substantially possible to maintain the temperature of a space in which the water tank is installed, at a constant temperature. Thus, an immersion heater that maintains water in the water tank in a set temperature range is installed.
When briefly describing a general structure of the immersion heater, the immersion heater includes a heat generation tube for generating heat and a controller that controls an operation of the heat generation tube. Although the shape of the above-described heat generation tube varies according to a required heat generation condition or the size of the water tank, the heat generation tube is mostly wound in the form of a coil having a predetermined diameter, is formed in the range of a length at which the heat generation tube can be installed in the water tank, and is connected to the above-described controller. A water temperature detection sensor for detecting a water temperature and a heat generation tube detection sensor for detecting the temperature of the heat generation tube are respectively installed adjacent to the heat generation tube.
The above-described water temperature detection sensor and heat generation tube detection sensor are installed to detect the water temperature and the temperature of the heat generation tube and to stop an operation of the heat generation tube when the detected water temperature and temperature of the heat generation tube are out of an allowable range. For example, the above-described water temperature and heat generation tube detection sensors are configured to have a structure in which well-known sensing members for detecting heat are self-shorted due to the temperature of water or a solution in the heat generation tube or the water tank and a current applied to the heat generation tube is cut off by the above-described controller.
In this case, a power wire and a sensor wire, which are disposed to deliver currents and to transmit signals, are connected to the heat generation tube and the detection sensors. However, there is a problem that water flows into a portion into which the power wire and the sensor wire are inserted and a short circuit occurs. Thus, in the conventional immersion heater, the portion into which the power wire and the sensor wire are inserted should be placed on the surface of water. Thus, there is a limitation in utilization. In order to solve the problem, a scheme for sealing the portion into which the power wire and the sensor wire are inserted, with silicone or packing, has been suggested. However, in a currently-suggested sealing technique, the inflow of water along the power wire and the sensor wire cannot be completely prevented.